434 SCIENCE PROGRESS. 



does not exhibit it. Here the explosive disturbance of the 

 active state is accompanied by diminished susceptibility to 

 respond to a stimulus, in other words, diminished excita- 

 bility. The study of the precise conditions which affect 

 the restoration of excitability and of functional capacity 

 might be illustrated by many instances drawn from the 

 physiology of muscle and nerve. It will be sufficient in an 

 article of this character to indicate that the whole subject 

 is treated in the most suggestive manner by Prof. Bieder- 

 mann, and should afford valuable help to any who desire 

 to ascertain how far modern physiology has succeeded in 

 the investigation of such a fundamental vital attribute as 

 the property of returning from the active to the resting state. 



One other point of general interest is brought into 

 prominence by the study of muscle and nerve now before 

 us, namely, " functional capacity ". 



From the above remarks it will be gathered that "func- 

 tional capacity " implies the capability of the tissue to 

 undergo a change resulting in definite new effects those 

 of activity, whilst " excitability " implies the susceptibility of 

 the tissue to enter upon this change on receipt of a stimulus. 

 At first sight the two phrases seem to be identical, but a 

 little consideration will show that they are not, although it 

 must be admitted that the significance of their separation 

 has been only grasped during the last decade, mainly through 

 the work of Hering and of Biedermann. The measure of 

 functional capacity is the comparative amount of active 

 display which the tissue is capable of showing, the extent 

 and force of its excitatory explosion ; the measure of 

 excitability is the comparative ease with which it may be 

 forced to enter upon its functional active state. Nerve is 

 the most excitable of all tissue, and thus affords the best in- 

 stances of the distinction just referred to. It may be 

 rendered less excitable, but of increased functional capacity, 

 by the passage of a weak voltaic current, this change oc- 

 curring at the point of entry, or anode, during the current 

 flow. On the other hand, it is more excitable but of 

 diminished functional capacity at the point of exit, or 

 cathode, of this current. Many other instances might be 



